The predictive value of the hypoxia altitude simulation test (HAST) or other baseline values to predict altitude-related adverse health effects (ARAHE) is not established. To address this gap, the main goals of this investigation will be 1) to evaluate the diagnostic accuracy of the HAST in identifying individuals that will experience ARAHE during altitude travel and 2) to establish prediction models incorporating other commonly assessed clinical characteristics either alone or in combination with the HAST as predictors of ARAHE in altitude travelers.

Hypotheses: In lowlanders with COPD, a PaO2 <6.6 kPa or another cutoff of PaO2 or SpO2 at the end of the HAST, at rest or during exertion and/or clinical variables including symptoms, pulmonary function indices, 6-min walk distance (6MWD), either alone or combined to a multivariable model, will predict ARAHE during a sojourn of 2 days at 3100m with accuracy greater than chance

Altitude or air travel has become increasingly popular for recreational and professional reasons. Chronic obstructive pulmonary disease (COPD) affects up to 12% of adults worldwide and is associated with progressive hypoxemia, especially during exercise, due to respiratory mechanical constraints, airway obstruction and increasing pulmonary hypertension (PH). COPD patients are at increased risk of ARAHE including acute mountain sickness (AMS) and severe hypoxemia. Factors assessed at lowland that would predict ARAHE of COPD patients exposed to a hypobaric hypoxic environment at altitude or during air travel would be highly warranted. During the HAST COPD-patients are exposed to an inspiratory oxygen fraction (FiO2) of 15.1% corresponding to an altitude of ≈ 2500m and this test was designed to predict deoxygenation at altitude. The predictive value of the HAST or other baseline values to predict ARAHE is not established. To address this gap, the main goals of this investigation will be 1) to evaluate the diagnostic accuracy of the HAST in identifying individuals that will experience ARAHE during altitude travel and 2) to establish prediction models incorporating other commonly assessed clinical characteristics either alone or in combination with the HAST as predictors of ARAHE in altitude travelers.

For this diagnostic accuracy study, COPD-patients with an FEV1 40-80% predicted living < 1000 m without severe hypoxemia (SpO2, <92%), hypercapnia (PaCO2 >6 kPa) or comorbidities will be recruited to traveling to and staying for two nights at 3100 m. At 760 m, the HAST will be performed, at 760 m and 3100 m symptoms, vital signs, SpO2, pulmonary function tests, 6MWD, sleep studies will be repetitively assessed. ARAHE will be defined if one of the following present: AMS with a Lake Louise questionnaire score >4 including headache, or AMSc score ≥0.7, resting SpO2 <80% >30 min or <75% for >15 min; or exercise SpO2 <75% for >5 min accompanied by symptoms, any intercurrent illness including infections, hypertension, neurologic impairments, dyspnea or discomfort at rest requiring oxygen treatment, chest pain and/or ECG signs of cardiac ischemia.

Inclusion Criteria:

• Men and women, age 35-75 y, living at low altitude (<800 m).
• COPD diagnosed according to the Global Initiative for Obstructive Lung Disease (GOLD) guidelines, FEV1 40-80% predicted, pulse oximetry ≥92%, PaCO2 <6 kPa, breathing ambient air at 760 m.

Exclusion Criteria:

• COPD exacerbation, very severe COPD with hypoxemia or hypercapnia at 760 m (see above).
• Other lung disease, relevant comorbidities (such as uncontrolled cardiovascular disease, i.e., unstable arterial hypertension, coronary artery disease; previous stroke; obesity (body mass index >35 kg/m2); internal, neurologic, rheumatologic or psychiatric disease; current heavy smoking (>20 cigarettes per day).
• Renal failure and/or allergy to sulfonamides.

COPD-patients living in the Bishkek area (mean altitude 760m) will be recruited among patients of the outpatient clinic of the National Center for Cardiology and Internal Medicine.